Uploaded January 2025 | Updated September 2026, 2 weeks ago
Fastest SSD For Your M4 Mac Thunderbolt 5 Enclosure - Samsung 990 Pro vs WD SN850X Write Speed Test.
So having mentioned the cache issues with the Samsung 990 Pro 4TB in previous videos, I thought it would be good to show this in a comparison with the WD SN850X 4TB. I used the M4 Max MacBook Pro for the tests as it has Thunderbolt 5.
The Samsung 990 Pro 4TB only has about 442GB of fast pSLC cache. pSLC meaning pseudo SLC. For a 4TB SSD I think this cache is on the low side. Once the cache is exhausted the write speed drops to about 1.6GB/s and lower.
While I can't find definitive information on how big the cache is on the WD SN850X 4TB, which is also pSLC. The 1TB version has 300GB of cache and the 2TB has 600GB. In my own usage, the 4TB version does not exhaust its cache when moving a folder of over one 1TB. This suggests to me that that the cache scales, which is evident with the scaling of the cache between the 1TB and 2TB versions. So given that the 4TB can easily handle just over 1TB without exhausting its cache, I think it's safe to say that it has 1200MB or 1.2TB of cache.
When the WD SN850X 4TB does exhaust its cache and drops to the its slower write speed. It's not only faster than the slower speed of the Samsung 990 Pro, at about 1700MB/s but it also has bursts up to about 2400MB/s. This indicates that the WD SN850X 4TB has a faster recovery time for its cache compared to the Samsung 990 Pro 4TB.
Don't forget, my tests for these SSDs are as storage drives inside external Thunderbolt 4, Thunderbolt 5 and USB4 enclosures for use with Mac computers. So while the Samsung 990 Pro 4TB may have some advantages as a system boot drive. As a storage SSD inside an enclosure, the WD SN850X clearly has the advantage.
As for the Acasis TB501. Some people may be indifferent to me calling it a Thunderbolt 5 enclosure and that it is recognised as a USB4 V2 device under macOS. However, it does have an Intel JHL9480 controller, which is a Thunderbolt 5 controller and it does run at 80Gb/s for data transfer.
Here's a link to my ACASIS products playlist:
youtube.com/playlist?list=PLleKChtNUwZRKLTq5fpaZ5w72z5FlQCF9
Here's a link to my SSD build and speed test playlist:
youtube.com/playlist?list=PLleKChtNUwZQvaYS9r0zHvkaTXSYlnX6q
Use my promo code David15 for a 15% discount if buying from the Acasis website.
Acasis website
TB501 enclosure ➡ bit.ly/4fsUfEQ
TBU405Pro M1 Enclosure ➡ bit.ly/4i1edsR
TBU401 enclosure ➡ bit.ly/49PFnPu
Acasis on Amazon
TB501 enclosure ➡ Not available yet on Amazon
TBU405Pro M1 Enclosure ➡ amzn.to/41V6p62
TBU401 enclosure ➡ amzn.to/3DwYEta
WD SSDs:
SN850X 4TB ➡ geni.us/SN850X-4TB
SN850X 2TB ➡ geni.us/SN850X-2TB
SN850X 1TB ➡ geni.us/SN850X-1TB
Links to Apple products:
M4 Max MacBook Pro 16" ➡ geni.us/70Xn
M4 Max MacBook Pro 14" ➡ geni.us/57QzTfu
M4 Pro MacBook Pro 16" ➡ geni.us/qSYR
M4 Pro MacBook Pro 14" ➡ geni.us/4thf yu0
M4 MacBook Pro 14" ➡ geni.us/Y7TFR
Mac Mini M4 ➡ geni.us/oibaLH
Mac Mini M4 Pro ➡ geni.us/ImJto
Video chapters:
00:00 Intro & explanation
01:31 WD SN850X test
04:14 Samsung 990 Pro test
09:25 End summary
AMAZON ASSOCIATE DISCLOSURE:
I am an Amazon Associate.
My Amazon links are Amazon affiliate links.
I earn money from qualifying purchases when you use my Amazon affiliate links.
OTHER EARNINGS AND COMMISSIONS:
I also earn money from other product links within my video description.
For the sake of clarity and for the avoidance of any confusion, assume that I earn money from commissions from any and all links that I have within my video description.
Amazon links to stuff used in this video:
The gear that I use, have used or reviewed that I would recommend.
Cameras: amzn.to/3PzC8mI
Microphones: amzn.to/3tD6FaM
Computers: amzn.to/3tuwHNr
Phones: amzn.to/3ttqjWN
iPads & Tablets: amzn.to/46t8wxG
You can also send me a coffee donation via PayPal if you found my video super helpful:
paypal.me/DavidHarry
My Amazon pages with videos and product links:
Amazon USA amazon.com/shop/davidharry
Amazon UK amazon.co.uk/shop/davidharry
If you would like to help my channel please use my global Amazon Affiliate links. I will be paid a small commission for anything you buy from Amazon when using these links. These commissions don't cost you any extra but really do help me to buy gear for my productions and to review:
Amazon USA: geni.us/Amazon-USA
Amazon UK: geni.us/Amazon-UK
Amazon Deutschland: geni.us/Amazon-Deutschland
Amazon France: geni.us/Amazon-France
Amazon España: geni.us/Amazon-Espana
Amazon Canada: geni.us/Amazon-Canada
Contact for product reviews: YouTube@DavidHarry.com
I’m David Harry. Thank you very much for watching this video, take care and goodbye now.
Cheers,
Dave.
Fastest SSD For Your M4 Mac Thunderbolt 5 Enclosure - Samsung 990 Pro vs WD SN850X Write Speed Test.
So having mentioned the cache issues with the Samsung 990 Pro 4TB in previous videos, I thought it would be good to show this in a comparison with the WD SN850X 4TB. I used the M4 Max MacBook Pro for the tests as it has Thunderbolt 5.
The Samsung 990 Pro 4TB only has about 442GB of fast pSLC cache. pSLC meaning pseudo SLC. For a 4TB SSD I think this cache is on the low side. Once the cache is exhausted the write speed drops to about 1.6GB/s and lower.
While I can't find definitive information on how big the cache is on the WD SN850X 4TB, which is also pSLC. The 1TB version has 300GB of cache and the 2TB has 600GB. In my own usage, the 4TB version does not exhaust its cache when moving a folder of over one 1TB. This suggests to me that that the cache scales, which is evident with the scaling of the cache between the 1TB and 2TB versions. So given that the 4TB can easily handle just over 1TB without exhausting its cache, I think it's safe to say that it has 1200MB or 1.2TB of cache.
When the WD SN850X 4TB does exhaust its cache and drops to the its slower write speed. It's not only faster than the slower speed of the Samsung 990 Pro, at about 1700MB/s but it also has bursts up to about 2400MB/s. This indicates that the WD SN850X 4TB has a faster recovery time for its cache compared to the Samsung 990 Pro 4TB.
Don't forget, my tests for these SSDs are as storage drives inside external Thunderbolt 4, Thunderbolt 5 and USB4 enclosures for use with Mac computers. So while the Samsung 990 Pro 4TB may have some advantages as a system boot drive. As a storage SSD inside an enclosure, the WD SN850X clearly has the advantage.
As for the Acasis TB501. Some people may be indifferent to me calling it a Thunderbolt 5 enclosure and that it is recognised as a USB4 V2 device under macOS. However, it does have an Intel JHL9480 controller, which is a Thunderbolt 5 controller and it does run at 80Gb/s for data transfer.
Here's a link to my ACASIS products playlist:
youtube.com/playlist?list=PLleKChtNUwZRKLTq5fpaZ5w72z5FlQCF9
Here's a link to my SSD build and speed test playlist:
youtube.com/playlist?list=PLleKChtNUwZQvaYS9r0zHvkaTXSYlnX6q
Use my promo code David15 for a 15% discount if buying from the Acasis website.
Acasis website
TB501 enclosure ➡ bit.ly/4fsUfEQ
TBU405Pro M1 Enclosure ➡ bit.ly/4i1edsR
TBU401 enclosure ➡ bit.ly/49PFnPu
Acasis on Amazon
TB501 enclosure ➡ Not available yet on Amazon
TBU405Pro M1 Enclosure ➡ amzn.to/41V6p62
TBU401 enclosure ➡ amzn.to/3DwYEta
WD SSDs:
SN850X 4TB ➡ geni.us/SN850X-4TB
SN850X 2TB ➡ geni.us/SN850X-2TB
SN850X 1TB ➡ geni.us/SN850X-1TB
Links to Apple products:
M4 Max MacBook Pro 16" ➡ geni.us/70Xn
M4 Max MacBook Pro 14" ➡ geni.us/57QzTfu
M4 Pro MacBook Pro 16" ➡ geni.us/qSYR
M4 Pro MacBook Pro 14" ➡ geni.us/4thf yu0
M4 MacBook Pro 14" ➡ geni.us/Y7TFR
Mac Mini M4 ➡ geni.us/oibaLH
Mac Mini M4 Pro ➡ geni.us/ImJto
Video chapters:
00:00 Intro & explanation
01:31 WD SN850X test
04:14 Samsung 990 Pro test
09:25 End summary
AMAZON ASSOCIATE DISCLOSURE:
I am an Amazon Associate.
My Amazon links are Amazon affiliate links.
I earn money from qualifying purchases when you use my Amazon affiliate links.
OTHER EARNINGS AND COMMISSIONS:
I also earn money from other product links within my video description.
For the sake of clarity and for the avoidance of any confusion, assume that I earn money from commissions from any and all links that I have within my video description.
Amazon links to stuff used in this video:
The gear that I use, have used or reviewed that I would recommend.
Cameras: amzn.to/3PzC8mI
Microphones: amzn.to/3tD6FaM
Computers: amzn.to/3tuwHNr
Phones: amzn.to/3ttqjWN
iPads & Tablets: amzn.to/46t8wxG
You can also send me a coffee donation via PayPal if you found my video super helpful:
paypal.me/DavidHarry
My Amazon pages with videos and product links:
Amazon USA amazon.com/shop/davidharry
Amazon UK amazon.co.uk/shop/davidharry
If you would like to help my channel please use my global Amazon Affiliate links. I will be paid a small commission for anything you buy from Amazon when using these links. These commissions don't cost you any extra but really do help me to buy gear for my productions and to review:
Amazon USA: geni.us/Amazon-USA
Amazon UK: geni.us/Amazon-UK
Amazon Deutschland: geni.us/Amazon-Deutschland
Amazon France: geni.us/Amazon-France
Amazon España: geni.us/Amazon-Espana
Amazon Canada: geni.us/Amazon-Canada
Contact for product reviews: YouTube@DavidHarry.com
I’m David Harry. Thank you very much for watching this video, take care and goodbye now.
Cheers,
Dave.
